Soluble material and process for three-dimensional modeling

ABSTRACT

A process for three-dimensional modeling in which an alkali-soluble thermoplastic material is used in an additive deposition process to form a soluble support structure ( 28 ) for a three-dimensional object ( 26 ) under construction. The alkali-soluble thermoplastic material includes a base polymer of carboxylic acid and a plasticizer. Following formation, the object ( 26 ) is placed in an alkaline bath to dissolve the support structure ( 28 ). The alkali-soluble material can be used to form an alkali-soluble three-dimensional object ( 26 ).

CROSS-REFERENCE TO RELATED APPLICATIONS

this application is United States national phase entry of PCTInternational Application No. US00/10592, filed on Apr. 19, 2000, whichclaims the benefit of U.S. Provisional Application No. 60/130,165, filedApr. 20, 1999.

BACKGROUND OF THE INVENTION

This invention relates to the fabrication of three-dimensional objectsusing additive process modeling techniques. More particularly, theinvention relates to forming three-dimensional objects by depositingsolidifiable material in a predetermined pattern and providing supportstructures to support portions of such a three-dimensional object as itis being built.

Additive process modeling machines make three-dimensional models bybuilding up a modeling medium, based upon design data provided from acomputer aided design (CAD) system. Three-dimensional models are usedfor functions including aesthetic judgments, proofing the mathematicalCAD model, forming hard tooling, studying interference and spaceallocation, and testing functionality. One technique is to depositsolidifiable modeling material in a predetermined pattern, according todesign data provided from a CAD system, with the build-up of multiplelayers forming the model.

Examples of apparatus and methods for making three-dimensional models bydepositing layers of solidifiable modeling material from an extrusionhead are described in Crump U.S. Pat. No. 5,121,329, Batchelder, et al.U.S. Pat. No. 6,303,141, Crump U.S. Pat. No. 5,340,433, Batchelder, etal. U.S. Pat. No. 5,402,351, Danforth, et al. U.S. Pat. No. 5,738,817,Batchelder, et al. U.S. Pat. No. 5,764,521 and Swanson et al. U.S. Pat.No. 6,004,124, all of which are assigned to Stratasys, Inc., theassignee of the present invention. The modeling material may be suppliedto the extrusion head in solid form, for example in the form of aflexible filament wound on a supply reel or in the form of a solid rod,as disclosed in U.S. Pat. No. 5,121,329. As described in U.S. Pat. No.4,749,347, modeling material may alternatively be pumped in liquid formfrom a reservoir. In any case, the extrusion head extrudes moltenmodeling material from a nozzle onto a base. The extruded material isdeposited layer-by-layer in areas defined from the CAD model. Asolidifiable material which adheres to the previous layer with anadequate bond upon solidification is used as the modeling material.Thermoplastic materials have been found particularly suitable for thesedeposition modeling techniques.

Examples of apparatus and methods for making three-dimensional models bydepositing solidifiable material from a jetting head are described, forexample, in Helinski U.S. Pat. No. 5,136,515, Masters U.S. Pat. No.4,665,492 and Masters U.S. Pat. No. 5,216,616. Particles are directed tospecific locations in a predetermined pattern as defined by a CAD model,and deposited and built up to construct the desired object.

In creating three dimensional objects by additive process techniques,such as by depositing layers of solidifiable material, it is the rulerather than the exception that supporting layers or structures must beused underneath overhanging portions or in cavities of objects underconstruction, which are not directly supported by the modeling materialitself. For example, if the object is a model of the interior of asubterranean cave and the cave prototype is constructed from the floortowards the ceiling, then a stalactite will require a temporary supportuntil the ceiling is completed. Support layers or structure may berequired for other reasons as well, such as allowing the model to beremoved from a base, resisting a tendency for the model to deform whilepartially completed, and resisting forces applied to a partiallycompleted model by the construction process.

A support structure may be built utilizing the same depositiontechniques and apparatus by which the modeling material is deposited.The apparatus, under appropriate software control, produces additionalgeometry acting as a support structure for the overhanging or free-spacesegments of the object being formed. Support material is depositedeither from a separate dispensing head within the modeling apparatus, orby the same dispensing head that deposits modeling material. The supportmaterial is chosen so that it adheres to the modeling material.Anchoring the model to such support structures solves the problem ofbuilding the model, but creates the additional problem of removing thesupport structure from the finished model without causing damage to themodel.

The problem of removing the support structure has been addressed byforming a weak, breakable bond between the model and the supportstructure, such as is described in Crump, et al. U.S. Pat. No.5,503,785. The '785 patent discloses a process by which a material thatforms a weak, breakable bond with the modeling material is selected as arelease material. The release material is deposited along the interfacebetween the object and its support structure in a layered fashion or asa coating, permitting the support structure to be broken away afterformation of the object. The support structure may be formed of themodeling material or it may be formed of the release material.

The '785 patent discloses various combinations of materials that may beused as modeling and release materials. For instance, the '785 patentdiscloses that a soluble release material may be utilized, so that anysuch material remaining on the model after the support is broken awaycan be removed by placing the model in a bath. Water soluble wax,polyethylene oxide and glycol-based polymers, polyvinylpyrrolidone-based polymers, methyl vinyl ether, maleic acid-basedpolymers, polyoxazoline-based polymers and polyquaternium II aredisclosed, as well as solvent-soluble acrylates and stearic and azelaicacids. Soluble supports can eliminate scarring of the model surface andthe need to use force in removing supports.

In extrusion based systems, a variation of applying release material inlayers has been implemented, in which the release material is applied inshort bead segments (termed “perforations”) between the supportstructure and the model under construction. The perforations reduceadhesion of the support layer by limiting the area of contact with themodel, to aid in the removal of breakaway supports.

There is a continuing need to provide a support structure that releasesfrom a three-dimensional model without the application of force and thatwill not mar the model surface finish, and that further has goodmechanical strength and is compatible with the modeling process and themodeling material.

BRIEF SUMMARY OF THE INVENTION

The present invention is an improved deposition modeling process whichuses an alkali-soluble thermoplastic material for forming analkali-soluble support structure for a three-dimensional object underconstruction or for forming an alkali-soluble three-dimensional object.The alkali-soluble material comprises a base polymer containing acarboxylic acid, and a plasticizer. In the preferred embodiment, thecarboxylic acid is methacrylic acid and the base polymer furthercontains an alkyl methacrylate, preferably methyl methacrylate. Thealkyl methacrylate comonomer provides thermal and toughness propertiessuitable for depositing modeling, while the plasticizer reduces theviscosity and increases the melt flow index of the base polymer. Asupport structure or object formed from the alkali-soluble thermoplasticmaterial dissolves when placed in an alkaline bath.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagrammatic illustration of a model formed by afilament-feed extrusion apparatus using the alkali-soluble material ofthe present invention as a support structure.

FIG. 2 is a perspective view (portions broken away) of the model of FIG.1 in an alkaline bath used in practicing the process of the presentinvention.

DETAILED DESCRIPTION

The process of the present invention employing an alkali-solublethermoplastic material is applicable for use in three-dimensionalmodeling systems which deposit molten modeling material that solidifiesto form an object.

The present invention is described with reference to a depositionmodeling system of the type disclosed in U.S. Pat. No. 5,121,329 andU.S. Pat. No. 6,004,124, which are hereby incorporated by reference asif set forth fully herein. In the described embodiment, the modelingmaterial and the support material are deposited as substantiallycontinuous strands layer-by-layer from an extrusion head and aresupplied to the extrusion head in the form of a flexible filament. Itwill be understood by those skilled in the art that the invention can bepracticed with advantage in various other types of modeling machines aswell, and that the materials may be supplied in alternative forms, suchas a liquid, solid rod, pellet or granulated form.

FIG. 1 shows an extrusion apparatus 10 building a model 26 supported bya support structure 28 according to the present invention. The extrusionapparatus 10 includes an extrusion head 12, a material-receiving base14, a filament supply spool 16 and a control 18. Extrusion head 12 movesin X and Y directions with respect to base 14, which moves in a verticalor Z direction. Supply spool 16 supplies a flexible filament 20 toextrusion head 12. Filament 20 typically follows a rather tortuous paththrough extrusion apparatus 10, and is advanced towards extrusion head12 by means of stepper motor-driven pinch rollers. Filament 20 is meltedin a liquifier 22, carried by extrusion head 12. The liquifier 22 heatsthe filament to a temperature slightly above its solidification point,reducing it to a molten state. Molten material is extruded through anorifice 24 of liquifier 22 onto base 14.

The extrusion apparatus 10 of the disclosed embodiment has no positivecut-off valve for stopping flow of the molten material through orifice24 when a layer or a pass is complete. The flow is stopped by ceasing toadvance filament 20 into extrusion head 12. The flow rate at which themolten material is dispensed onto base 14 is determined by a combinationof the orifice size and the rate at which filament 20 is advanced intoextrusion head 12.

The movement of extrusion head 12 is controlled by control 18 so as todeposit material onto base 14 in multiple passes and layers to buildthree-dimensional model 26 having a shape determined by stored CAD dataand further to build support structure 28 defined so as to physicallysupport the model 26 as it is being built. The model 26 and Its supportstructure 28 are built up on the base 14 within a build envelope havingan environment controlled to promote solidification. A first layer ofthe deposited material adheres to the base so as to form a foundation,while subsequent layers of material adhere to one other. A base that hasbeen successfully used is a polymer foam removably mounted to aplatform. Other materials that may serve as a base include sandpaperformed of a fine wire mesh screen coated with sand and adhered to aplatform, a water-soluble wax, a foam plastic material, and an acrylicsheet mounted to a vacuum platen.

A modeling material A is dispensed to form the model 26. Analkali-soluble support material B is dispensed in coordination with thedispensing of modeling material A to form the support structure 28. Forconvenience, the extrusion apparatus 10 is shown with only one filamentsupply spool 16 providing a single filament 20. It should be understood,however, that in the practice of the present invention using afilament-feed apparatus such as disclosed herein the modeling material Aand the alkali-soluble support material B are provided to the extrusionapparatus 10 on separate filament supply spools. The extrusion apparatus10 may then accommodate the dispensing of two different materials by:(1) providing two extrusion heads 12, one supplied with modelingmaterial A and one supplied with modeling material B (such as isdisclosed in the '124 patent); (2) providing a single extrusion headsupplied with both the modeling material A and the alkali-supportmaterial B, with a single nozzle for dispensing both materials (such asshown in FIG. 6 of the '329 patent); or (3) providing a single extrusionhead supplied with both materials, with each material dispensed througha separate nozzle (such as shown in FIG. 6 of the '785 patent).

Modeling material A is typically a thermoplastic material that can beheated relatively rapidly from a solid state to a predeterminedtemperature above the solidification temperature of the material, andpreferably has a relatively high tensile strength. Anacrylonitrile-butadiene-styrene (ABS) composition is one particularlysuitable modeling material. Other materials that may be used for themodeling material A include a variety of waxes, paraffin, a variety ofthermoplastic resins, metals and metal alloys. Glass and chemicalsetting materials, including two-part epoxies, would also be suitable.

Support material B of the present invention is a thermoplastic solublein an alkaline solution, as described in more detail below.Alkali-soluble support material B likewise can preferably be heatedrelatively rapidly from a solid state filament to a predeterminedtemperature above the solidification temperature of the material, andsolidify upon a drop in temperature after being dispensed.

The soluble support structure 28 created with support material B may beformed in a known manner, such as disclosed in U.S. Pat. No. 5,503,785,which is hereby incorporated by reference as if set forth fully herein.FIGS. 3-5 of the '785 patent illustrate a removable support structure.As shown in FIG. 1 herein, the support structure 28 may be builtentirely out of the support material B. Or, as shown and described inthe '785 patent, the alkali-soluble support material B may form adissolvable joint between the model formed of modeling material A and asupport structure formed of the same material A. The joint can be arelease layer or layers, or a thin coating.

After completion of the model 26, the support structure 28 is removedfrom the model 26 by soaking the model 26 with its attached supportstructure 28 in a bath 40 containing a alkaline solution C. In theembodiment shown in FIG. 2, bath 40 is an ultrasonic,temperature-controlled bath which contains a removable mesh basket 42for holding the model 26. The temperature of bath 40 is set using atemperature control 44. The alkaline solution C is an aqueous solutionthat can be washed down the drain for disposal. The temperature of thesolution C in bath 40 can be heated to speed dissolution of supportmaterial B. An ultrasonic frequency generator 46 having an on/off switchstarts and stops the ultrasonic transmission. The ultrasonic frequencytransmission generates air bubbles which assist in dissolving away thesupport material B by vibrating the model.

Model 26 remains in bath 40 until the support material B dissolves. Thebasket 42 is then removed from bath 40. The basket 42 can be placed in asink and the solution C rinsed off of the model 26 with water and washeddown the drain. Bath 40 has a drain 48 from which a plug is removed todrain the solution C from the bath 40.

As an alternative to removing support structure 28 from the model 26 bydissolving the support material B in a bath, the support material may bedissolved using water jets operated by hand or by automation.

The base 14 may be removed from the model 26 before placing the model inthe bath 40. Alternatively, the base 14 may remain adhered to model 26as it is placed in bath 40. In the latter case, an alkali-soluble basemay be desired, such as an alkali-soluble foam.

The alkali-soluble support material B must satisfy a large number ofmodeling criteria for the particular modeling system in which it isused, relating generally to thermal properties, strength, viscosity andadhesion. As to thermal properties, the support material B must notdeform at the temperature in the build envelope, so as to maintainstructural fidelity of the model that it supports. It is thereforedesired that the support material B have a glass transition temperature(T_(g)) at least 10° C. above the build envelope temperature. Further,if the glass transition temperature of support material B is lower thanthat of modeling material A, the rate of dissolution of support materialB may be increased by temperature control.

The support material B must have a melt viscosity suitable for themodeling process. In a modeling system of the type described herein, themelt viscosity must be low enough at the liquifier temperature so thatit can be extruded through the orifice of the liquifier as a generallycontinuous strand or bead and so that deposited strands or beads ofsupport material B have little melt strength, allowing them to lay flatrather than curl up. Melt viscosity is lowered by increasing thetemperature in the liquifier. Too high a liquifier temperature, however,can cause material sitting idle in the liquifier to decompose. Ifdecomposed, in the case of an extrusion head that has no positivecut-off mechanism, support material B will drain uncontrollably from theliquifier into the build envelope, a condition referred to as “ooze”. Inpractice, viscosity may be measured by its inverse parameter, melt flow.A desirable melt flow index for support material B is greater than about1 g/10 minutes, as measured by ASTM D1238, under a load of 1.2 kg at230° C., and is preferably between 5-10 g/10 minutes.

To properly support the model under construction, the support material Bmust bond to itself (self-laminate) and bond weakly to modeling materialA (co-laminate). Where the support structure is built up from the base,support material B must additionally bond to the base 14. The acidcontent in support material B of the present invention makes thematerial fairly sticky, so that it will adequately adhere to a base madeof any number of materials. For example, a polyurethane foam base hasbeen successfully utilized in the practice of the invention.

To produce an accurate model, support material B must also exhibitlittle shrinkage upon cooling in the conditions of the build envelope,or, the shrink characteristics must match those of modeling material A.A shrink differential in the materials would cause stresses and bondfailures along the model/support structure joint.

Support material B must have sufficient mechanical strength in solidform to provide support to a model during its formation. The supportmaterial B must resist forces by the modeling material A, or the modelwill exhibit undesirable curling and deformation. Additionally, supportmaterial B, when supplied in filament or rod form, must be strong enoughto be shipped without breaking. When supplied in filament form, supportmaterial B must further have the strength and flexibility to be formedinto a filament, be spooled and unspooled, and be fed through theextrusion apparatus without breakage. Similarly, support material Bsupplied in filament form must have sufficient rigidity to not bedeformed by compressive forces during feeding through the extrusionapparatus. A tensile strength on the order of 1000-5000 psi is typicallyappropriate for deposition modeling applications.

Solubility characteristics required of support material B are that it bereadily soluble in an alkaline solution (pH 7 or higher) that does notadversely affect the modeling material A. It is additionally desirablethat the solution be non-toxic and non-flammable, so that it requires nospecial handling or disposal by users.

The thermoplastic soluble support material B of the present invention iscomprised of a base polymer and a plasticizer. The base polymer iscomprised of a first comonomer (which contains carboxylic acid) and asecond comonomer that is polymerized with the first comonomer (e.g., viafree-radical polymerization) to provide thermal and toughness propertiessuitable for deposition modeling. An alkyl methacrylate (includingmethyl, ethyl, propyl and butyl methacrylate), or a combination of alkylmethacrylates, is a suitable second comonomer. Other monomers may beused as the second comonomer, that achieve the thermal and toughnesscharacteristics desired for the modeling system in which the supportmaterial B will be used. A preferred base polymer is comprised ofmethacrylic acid as the first comonomer and methyl methacrylate as thesecond comonomer. The polymer is plasticized to attain Theologicalproperties desired for the modeling process.

A desirable amount of the acid-containing first comonomer is 15-60weight percent of the base polymer. The solubility of the supportmaterial B is due to the carboxylic acid in the base polymer. As theacid content of the base polymer increases, the required alkalinity (pH)of the alkaline solution used to dissolve it decreases. Optionally,additional monomers can be incorporated into the base polymer.

Selection of an appropriate plasticizer depends on a number of factors.The plasticizer must plasticate the dry base polymer into a processablethermoplastic meeting the desired criteria. A plasticizer reducesviscosity (increasing the melt flow index) and also lowers glasstransition temperature of a polymer. In addition, the plasticizer mustbe compatible with the base polymer. Compatibility is determined bypolarity, dispersion and hydrogen bonding forces, as shown by Small'ssolubility parameters of 8.0 or higher, preferably 8.5 or higher (usingSmall's molar attraction constant method), or as shown by Hansen'ssolubility parameters of 17.0, preferably 17.5 or higher (from Hansenmethod described in Handbook of Solubility Parameters, CRC Press (1991).The plasticizer must not exhibit exudation in the form of an oily filmon the plasticized polymer. The plasticizer must have a low vaporpressure at material processing and modeling temperatures, preferablyless than 10 mm Hg at 200° C. and less than 20 mm Hg at 250° C. Theplasticizer must additionally be hydrolyzable, soluble, emulsifiable ordispersable in an alkali solvating bath, pH 7 or higher.

Plasticizers found to be compatible include plasticizers in the generalclasses of dialkyl phthalates, cycloalkyl phthalates, benzyl and arylphthalates, alkoxy phthalates, alkyl/aryl phosphates, carboxylic acidesters, polyglycol esters, adipate esters, citrate esters, and esters ofglycerin. Commercially available plasticizers with specific structurefound to be compatible include:

Acetates:

cumyl phenyl acetate;

Glyceryl Triacetate, triacetin;

Adipates:

dibutoxy ethoxy ethyl adipate

dibutoxy ethyl adipate

di iso butyl adipate

Citrates:

tri-n-ethyl citrate;

acetyl tri-n-ethyl citrate;

tri-n-propyl citrate;

acetyl tri-n-propyl citrate;

tri-n-butyl citrate;

acetyl tri-n-butyl citrate;

Phthalates:

DBP, dibutyl phthalate (partial compatibility);

BBP, butyl benzyl phthalate (total compatibility);

DBEP dibutoxy ethyl phthalate (partial compatibility);

2 ethyl hexyl benzyl phthalate;

tetramethyl oxa onononyl benzyl phthalate;

Benzoates:

dipropylene glycol dibenzoate;

diethylene glycol dibenzoate;

50/50 blend dipropylene glycol dibenzoate and diethylene

glycol dibenzoate;

1,4 cyclohexane dimethanol dibenzoate;

glyceryl tribenzoate;

cumyl phenyl benzoate;

neopentyl glycol dibenzoate;

pentaerythritol tetabenzoate;

Phosphates:

butyl phenyl diphenyl phosphate;

TCP, tricresyl phosphate;

2 ethylhexyl diphenyl phosphate;

isodecyl diphenyl phosphate;

C12, C16 alkyl diphenyl phosphate;

isopropylated triphenyl phosphate;

Polyglycols:

Polyethylene glycols;

Polypropylene glycols.

Particularly preferred plasticizers have high thermal stability, andinclude: p-t-butylphenyl diphenyl phosphate; butyl benzyl phthalate;7-(2,6,6,8-tetramethyl-4-oxa-3-oxononyl) benzyl phthalate; C7/C9 alkylbenzyl phthalate; 2-ethylhexyl diphenyl phosphate; and isodecyl diphenylphosphate. Desirably, the plasticizer is added in amounts of between10-30 weight percent of the support material B.

Optionally, the support material B may contain other components as well,such as filler materials. For example, inert fillers may be selectedfrom a polymer filler group consisting of calcium carbonate, magnesiumcarbonate, glass spheres, graphite, carbon black, carbon fiber, glassfiber, talc, wollastonite, mica, alumina, silica, kaolin, whiskers andsilicon carbide. Inorganic fillers such as soluble salts may also beused.

Techniques conventional in polymer chemistry are used to compound thecomponent materials into support material B. The formulation may bemolded into rods, pellets or other shapes for use in the extrusionapparatus, or it may be used directly in the apparatus without priorsolidification. Alternatively, the mixture may be solidified and thengranulated, for supply to the extrusion apparatus in granulated form.For use in the modeling process shown and described herein, a granulatedfeedstock composition is processed through conventional extrusionapparatus to form continuous flexible filaments. Desirably, thesefilaments are wound in continuous lengths on a spool and dried. Supportmaterial B in filament form is supplied to the extrusion apparatus 10 asdescribed above. The filament 20 is typically of a very small diameter,on the order of 0.070 inches, and may be as small as 0.001 inches indiameter.

EXAMPLE I

The soluble thermoplastic composition contains 74 weight percent of thebase polymer and 26 weight percent of butyl phenyl diphenyl phosphateplasticizer. The base polymer consists of a higher and a lower molecularweight copolymer of methacrylic acid and methyl methacrylate. The basepolymer contains roughly 50 weight percent of the higher molecularweight copolymer and 50 weight percent of the lower molecular weightcopolymer, plus or minus 5 weight percent of each. Each copolymercontains a 1:2 weight percent ratio of methacrytic acid to methylmethacrylate. The higher molecular weight copolymer is characterized bya high viscosity (low melt flow), and the low molecular weight copolymeris characterized by a low viscosity (high melt flow). Melt flow of thecopolymers is measured by plasticizing each copolymer separately with 26weight percent of the butyl phenyl diphenyl phosphate plasticizer. Themelt flow index of the plasticized high molecular weight copolymer is inthe range of 0.4 to 0.8 g/10 minutes, as measured by ASTM D1238, 1.2 kgat 230° C. The melt flow index of the plasticized low molecular weightcopolymer is in the range of 28 to 35 g/10 minutes. The resultingthermoplastic composition has a melt flow index of 5-6.5 g/10 minutesand a glass transition temperature of about 90° C.

The thermoplastic is processed into a 0.070 inch diameter filament andwound on a spool. The filament is fed to a Stratasys FDM® 1650 or aStratasys FDM® 2000 benchtop model machine. Molten soluble thermoplasticis extruded from a liquifier having a temperature of 200° C. into a 70°C. build envelope onto a polyurethane foam base. The extrudedalkali-soluble thermoplastic has a road width of about 0.020 in. −0.040in. and a road height (slice interval) of about 0.007 in. −0.020 in. Amodel is built from ABS thermoplastic having a glass transitiontemperature of 104° C., using the alkali-soluble thermoplastic to formsupports. The model with the attached supports is placed into anultrasonic cleaning bath (having a scanning frequency of 25-27 Hz),containing an alkaline aqueous solution of approximately 98.7 weightpercent water, 0.85 weight percent water softener, 0.30 weight percentpH adjuster and 0.15 weight percent surfactant, resulting in a pH of 11to 13. The bath temperature is set to 70° C. (the bath temperature mustremain lower than the glass transition temperature of modeling materialA). In two hours time or less the supports are dissolved.

An alternative base polymer formulation combines the higher molecularweight 1:2 copolymer of methacrylic acid and methyl methacrylate with alower molecular weight copolymer containing 40 weight percentmethacrylic acid and 60 weight percent butyl methacrylate. A furtheralternative base polymer formulation uses acrylic acid as the firstcomonomer. The further alternative was found unacceptable for use in theStratasys FDM® modeling machines, however, as it results in a basepolymer having a lower glass transition temperature lower than the buildenvelope temperature of the machines.

EXAMPLE II

The alkali-soluble thermoplastic material contains 79+/−five weightpercent of the base polymer and 21 weight percent+/−5 weight percent ofbutyl phenyl diphenyl phosphate plasticizer. The base polymer consistsof a 1:1 weight percent ratio of methacrylic acid to methylmethacrylate, having a molecular weight of 135,000 grams/mole. Prior tocompounding the base polymer with the plasticizer, the base polymer Isheated in a 220° C. oven at low pressure to rid the polymer of water.Heating at low pressure for 10-15 hours was found sufficient to dry thebase polymer. The resultant dry polymer is in the form of granules,which are fed into a compounder with the plasticizer in a known manner.The resulting composition has a melt flow index in the range of 5-6.5g/10 minutes at 230° C. The glass transition onset temperature of thecomposition is about 101.5° C. and the glass transition peak temperatureis about 111° C.

As in Example I above, the composition is processed into a 0.070 inchdiameter filament and wound on a spool. The filament is fed to aStratasys FDM® 1650 or a Stratasys FDM® 2000 benchtop model machine.Molten soluble thermoplastic is extruded from a liquifier having atemperature of 235° C. into a build envelope having a temperature of 70°C. to 80° C., onto a polyurethane foam base. The extruded alkali-solublethermoplastic has a road width of about 0.020 in. −0.040 in. and a roadheight (slice interval) of about 0.007 in.−0.020 in. A model is builtfrom ABS thermoplastic having a glass transition temperature of 104° C.,using the alkali-soluble thermoplastic to form supports. To dissolve thesupports, the model is placed into an ultrasonic cleaning bath set to70° C. and having a scanning frequency of 25-27 Hz, containing analkaline aqueous solution of approximately 98.7 weight percent water,0.85 weight percent water softener, 0.30 weight percent pH adjuster and0.15 weight percent surfactant. In two hours time or less the supportsare dissolved. The alkali-soluble thermoplastic according to thisexample exhibits thermal properties, mechanical strength, viscosity,adhesion, solubility and processing characteristics suitable forthree-dimensional modeling on the Stratasys filament-feed benchtopmachines.

EXAMPLE III

The alkali-soluble thermoplastic material has the same composition as inExample II above, but in this example the base polymer is not heated torelease moisture. The thermoplastic material is processed and extrudedfrom a Stratasys FDM® machine as in Example II, and deposited to form asupport structure for a model built of ABS thermoplastic. In thisexample, the support material exhibited a greater amount of “ooze” fromthe extrusion head than is desirable, but otherwise exhibitedcharacteristics suitable for three-dimensional modeling. The “ooze” isattributable to water present in the composition. If used in a modelingsystem wherein the material dispenser has a positive cut-off mechanism,the “ooze” effect exhibited in the Stratasys FDM® machine would notoccur and the material according to this Example III could beeffectively utilized.

Although the present invention has been described with reference topreferred embodiments, workers skilled in the art will recognize thatchanges may be made in form and detail without departing from the spiritand scope of the invention. For example, it will be appreciated thatinnumerable modifications may be made to the modeling process. It willfurther be appreciated that various modifications may be made to thecomposition. Also, the thermoplastic material of the present inventioncould be used to create an alkali-soluble three-dimensional objecthaving usefulness in various molding processes. For example, thealkali-soluble material can form a dissolvable master core in a cast orinjection process. The alkali-soluble material can likewise be used tocreate a mold (by deposition modeling or otherwise), which mold canlater be dissolved out of an object formed by molding processes.

What is claimed is:
 1. In a process for making a three-dimensionalobject by dispensing solidifiable modeling material in a predeterminedpattern so as to define the three-dimensional object in coordinationwith dispensing solidifiable support material so as to define a supportstructure for the three-dimensional object, the support structurethereby having portions thereof in contact with the object, theimprovement comprising: forming at least those portions of the supportstructure contacting the object from an alkali-soluble thermoplasticmaterial comprising: a base polymer containing a carboxylic acid; and aplasticizer.
 2. The process of claim 1, wherein the carboxylic acid ismethacrylic acid present in an amount between about 15 weight percentand 60 weight percent of the base polymer.
 3. The process of claim 2,wherein the base polymer further contains an alkyl methacrylate.
 4. Theprocess of claim 3, wherein the alkyl methacrylate is methylmethacrylate.
 5. The process of claim 4, wherein the base polymercontains between about a 1:1 to a 1:2 weight percent ratio ofmethacrylic acid to methyl methacrylate.
 6. The process of claim 4,wherein the alkali-soluble thermoplastic material contains between about84 weight percent and 74 weight percent of the base polymer and containsbetween about 16 weight percent and 26 weight percent of theplasticizer.
 7. The process of claim 1, wherein the base polymer furthercontains an alkyl methacrylate.
 8. The process of claim 2, wherein thealkali-soluble thermoplastic material contains between about 10 weightpercent and 30 weight percent of the plasticizer.
 9. The process ofclaim 8, wherein the plasticizer is p-t-butylphenyl diphenyl phosphate,butyl benzyl phthalate, 7-(2,6,6,8-tetramethyl-4-oxa-3-oxononyl) benzylphthalate, C7/C9 alkyl benzyl phthalate, 2-ethylhexyl diphenyl phosphateor isodecyl diphenyl phosphate.
 10. The process of claim 1, wherein thealkali-soluble thermoplastic material has a melt flow index of betweenabout 5 g/10 minutes and 10 g/10 minutes under a load of 1.2 kg at 230°C.
 11. The process of claim 1 and further comprising: removing thesupport structure after the object is made by placing the object in analkaline bath.
 12. The process of claim 11, wherein the step of removingthe support structure includes the step of generating an ultrasonicfrequency in the alkaline bath.
 13. The process of claim 11, wherein thestep of removing the support structure includes the step of heating thealkaline bath.
 14. An additive process for making three-dimensionalobjects, comprising: dispensing an alkali-insoluble modeling material ina predetermined pattern defining a three-dimensional object havingoverhanging portions that require support during formation; anddispensing an alkali-soluble support material in the space beneath theoverhanging portions of the three-dimensional object in coordinationwith the dispensing of the modeling material to form a three-dimensionalsupport structure for the object, the alkali-soluble support materialcomprising a base polymer containing between about 15 weight percent and60 weight percent of a carboxylic acid, and a plasticizer; whereby thealkali-soluble support material may be dissolved from thethree-dimensional object by application of an alkaline solution.
 15. Theprocess of claim 14, wherein the carboxylic acid is methacrylic acid.16. The process of claim 15, wherein the base polymer further containsan alkyl methacrylate.
 17. The process of claim 16, wherein the alkylmethacrylate is methyl methacrylate.
 18. The process of claim 17,wherein the base polymer contains between about a 1:1 to a 1:2 weightpercent ratio of methacrylic acid to methyl methacrylate.
 19. Theprocess of claim 17, wherein the alkali-soluble support materialcontains between about 84 weight percent and 74 weight percent of thebase polymer aid contains between about 16 weight percent and 26 weightpercent of the plasticizer.
 20. The process of claim 14, wherein thebase polymer further contains an alkyl methacrylate.
 21. The process ofclaim 14, wherein the alkali-soluble support material contains betweenabout 10 weight percent and 30 weight percent of the plasticizer. 22.The process of claim 21, wherein the plasticizer is p-t-butylphenyldiphenyl phosphate, butyl benzyl phthalate,7-(2,6,6,8-tetramethyl-4-oxa-3-oxononyl) benzyl phthalate, C7/C9 alkylbenzyl phthalate, 2-ethylhexyl diphenyl phosphate or isodecyl diphenylphosphate.
 23. The process of claim 14, wherein the alkali-solublethermoplastic material has a melt flow index of between about 5 g/10minutes and 10 g/10 minutes under a load of 1.2 kg at 230° C.
 24. In aprocess for making three-dimensional objects by depositing solidifiablematerial onto a base, the improvement comprising providing as thesolidifiable material an alkali-soluble thermoplastic comprising: a basepolymer containing a carboxylic acid; and a plasticizer.
 25. The processof claim 24, wherein the base is contained in a build envelopemaintained at a build envelope temperature and wherein the plasticizeris selected and present in an amount so as to increase the melt flowindex of the base polymer, while maintaining the glass transitiontemperature of the base polymer at a temperature high enough so that thesolidifiable material does not soften at the build envelope temperature.26. The process of claim 24, wherein the carboxylic acid is methacrylicacid present in an amount between about 15 weight percent and 60 weightpercent of the base polymer.
 27. The process of claim 26, wherein thebase polymer further contains an alkyl methacrylate.
 28. The process ofclaim 27, wherein the alkyl methacrylate is methyl methacrylate.
 29. Theprocess of claim 28, wherein the base polymer contains between about a1:1 to a 1:2 weight percent ratio of methacrylic acid to methylmethacrylate.
 30. The process of claim 28, wherein the solidifiablematerial contains between about 84 weight percent and 74 weight percentof the base polymer and contains between about 16 weight percent and 26weight percent of the plasticizer.
 31. The process of claim 25, whereinthe base polymer further contains an alkyl methacrylate.
 32. The processof claim 25, wherein the solidifiable material has a melt flow index ofbetween about 5 g/10 minutes and 10 g/10 minutes under a load of 1.2 kgat 230° C.
 33. The process of claim 26, wherein the solidifiablematerial contains between about 10 weight percent and 30 weight percentof the plasticizer.
 34. The process of claim 33, wherein the plasticizeris p-t-butylphenyl diphenyl phosphate, butyl benzyl phthalate,7-(2,6,6,8-tetramethyl-4-oxa-3-oxononyl) benzyl phthalate, C7/C9 alkylbenzyl phthalate, 2-ethylhexyl diphenyl phosphate or isodecyl diphenylphosphate.
 35. As an article of manufacture, a three-dimensional objectcomprised of an alkali-soluble thermoplastic material comprising: a basepolymer containing a carboxylic acid; and a plasticizer.
 36. The articleof claim 35, wherein the carboxylic acid is methacrylic acid present inan amount between about 15 weight percent and 60 weight percent of thebase polymer.
 37. The article of claim 36, wherein the base polymerfurther contains an alkyl methacrylate.